The present invention relates to circuitry for measuring the volume flowrate of a fluid in a pipe which has two magnet coils positioned on opposite sides of the pipe and at least one pair of electrodes mounted on the inner surface of the pipe symmetrical to a plane defined by the pipe axis and the common axis of the coils. Also included are an excitation circuit for the coils which produces aiding and opposing magnetic fields and an evaluation circuit connected to the electrodes which produces a measurement signal proportional to the volumetric flowrate.
Circuitry of this type is known from German Patent 2 743 954. The use of opposing magnetic fields serves to recognize the presence of a non-symmetrical flow profile and is used to correct the flow signal. According to the European Patent Application 90 106 783 (not yet published), this method also serves to determine whether the pipe is full or not.
In the known circuits, it is possible that saturation may occur, which produces unstable signals due to electrochemical potential variations between the fluid and the electrodes.